Hemilabyrinthectomy causes both an increase and a decrease in corticotropin releasing factor mRNA in rat inferior olive

Corticotropin-releasing factor depolarizes rat lateral vestibular nuclear neurons through activation of CRF receptors 1 and 2

Corticotropin-releasing factor (CRF) is a neuropeptide mainly synthesized in the hypothalamic paraventricular nucleus and has been traditionally implicated in stress and anxiety. Intriguingly, genetic or pharmacological manipulation of CRF receptors affects locomotor activity as well as motor coordination and balance in rodents, suggesting an active involvement of the central CRFergic system in motor control. Yet little is known about the exact role of CRF in central motor structures and the underlying mechanisms. Therefore, in the present study, we focused on the effect of CRF on the lateral vestibular nucleus (LVN) in the brainstem vestibular nuclear complex, an important center directly contributing to adjustment of muscle tone for both postural maintenance and the alternative change from the extensor to the flexor phase during locomotion. The results show that CRF depolarizes and increases the firing rate of neurons in the LVN. Tetrodotoxin does not block the CRF-induced depolarization and inward current on LVN neurons, suggesting a direct postsynaptic action of the neuropeptide. The CRF-induced depolarization on LVN neurons was partly blocked by antalarmin or antisauvagine-30, selective antagonists for CRF receptors 1 (CRFR1) and 2 (CRFR2), respectively. Furthermore, combined application of antalarmin and antisauvagine-30 totally abolished the CRF-induced depolarization. Immunofluorescence results show that CRFR1 and CRFR2 are co-localized in the rat LVN. These results demonstrate that CRF excites the LVN neurons by co-activation of both CRFR1 and CRFR2, suggesting that via the direct modulation on the LVN, the central CRFergic system may actively participate in the central vestibular-mediated postural and motor control.

Spatial distribution of corticotropin-releasing factor immunopositive climbing fibers in the mouse cerebellum: analysis by whole mount immunohistochemistry

This study examined the spatial organization of corticotropin-releasing factor (CRF) immunopositive climbing fibers in the mouse cerebellum by whole mount immunohistochemistry. A striking pattern of parasagittal stripes of CRF staining was revealed. Cryosections of whole mount CRF stained cerebellum showed that anti-CRF immunostaining is restricted to climbing fibers in the molecular layer and does not penetrate deeper into the granular layer. The array of CRF stripes was reminiscent of zebrin II immunopositive Purkinje cell stripes in the anterior vermis and the hemispherical lobules. However, a direct comparison of the two distributions showed that the CRF-defined parasagittal stripes and transverse zones in the posterior vermis are different from those defined by the expression of zebrin II: in particular, CRF immunostaining revealed a transverse boundary between lobules VIb and VII and the presence of four CRF-immunopositive climbing fiber stripes in lobule VIII. Furthermore, an array of CRF stripes was seen in lobule X, the flocculus and the paraflocculus, despite uniform zebrin II expression in these areas. In these cases some, but not all, CRF-immunopositive stripes shared boundaries with Purkinje cell stripes that were visualized by the expression of heat shock protein 25. The results reveal a reproducible pattern of CRF-immunopositive climbing fiber innervation in the mouse cerebellum that bears a complex relationship to the stripes delineated by Purkinje cell compartmentation antigens.

Interaction between the hypothalamic-pituitary-adrenal axis and behavioural compensation following unilateral vestibular deafferentation

Vestibular compensation is defined as the process of behavioural recovery that occurs following the loss of sensory input from one or both vestibular labyrinths. The visual and postural instability resulting from the vestibular damage must alter the homeostasis of the subject; however, very little research has been conducted that investigates the interaction between vestibular compensation and the adaptive stress response of the body, i.e. the hypothalamic-pituitary-adrenal (HPA) axis. The aim of this review is to describe and evaluate the experimental evidence indicating a link between vestibular compensation and the body's response to stress, via the HPA axis.

Differential induction of brain-derived neurotrophic factor mRNA in rat inferior olive subregions following unilateral labyrinthectomy

Vestibular compensation, the neuronal process underlying behavioral recovery from vestibular dysfunction produced by unilateral labyrinthectomy, is attributed to functional reorganization of neuronal circuits in the brainstem and cerebellum. Climbing fibers originating from the inferior olive are suggested to play a crucial role in this compensatory process. To assess the possible contribution of brain-derived neurotrophic factor (BDNF) to the function of climbing fibers during vestibular compensation, we investigated the BDNF mRNA expression in the rat inferior olive after unilateral labyrinthectomy by quantitative in situ hybridization. We found several induction patterns depending on the subregions of the inferior olive 6 h after unilateral labyrinthectomy. First, in the dorsal cap and the ventrolateral outgrowth, the expression levels increased on the side contralateral to the lesion and decreased on the ipsilateral side. Second, in the beta nucleus, C subnucleus of the medial accessory olive, and A/B subnuclei of the medial accessory olive, we detected an increase in the mRNA expression level on the side contralateral to the lesion, but no changes in the expression level on the ipsilateral side. In the beta nucleus, where the strongest induction was observed, the mRNA expression level increased nearly five-fold. Third, in the dorsomedial cell column, the mRNA expression levels increased on both sides. Finally, we did not detect significant changes in mRNA expression levels in the other subregions of the inferior olive, the dorsal accessory olive, principal olive and rostral medial accessory olive. The changes in BDNF mRNA expression reverted to control levels by 72 h after the labyrinthectomy. The inferior olive subregions that showed changes in BDNF mRNA expression levels send climbing fibers to the cerebellar cortical regions that, in turn, project to the vestibular nuclei. Therefore, BDNF induced in these subregions could contribute to the functional reorganization of the olivo-cerebellar system for vestibular control.

Modulation by acute stress of chloride permeation across microdissected vestibular neurons membranes: different results in two rabbit strains and CRF involvement

Free hand isolation of adult rabbit vestibular Deiters' neurons and dissection of their single membranes allows the study of their ionic permeability characteristics in a microchambers device. In the case of hare-like rabbits, the dissection of such membranes presents evidence of a high basal permeation of labelled chloride, possibly related to mechanical disturbance of the plasma membrane-related cytoskeleton and activation of chloride channels. This did not apply to the laboratory strain of white New Zealand rabbits. However, membranes from hare-like rabbits which were stressed by being rotated on a platform before the experiment, behaved like those from the New Zealand strain. Vice versa, habituation to handling day after day of New Zealand rabbits resulted in a chloride permeation equal to that of unstressed hare-like rabbits. We propose that the stressful conditions result in the release of neurochemical messages to the vestibular Deiters' cells which influence their electrophysiological behavior. The corticotropin releasing factor (CRF), a stress-related peptide present in the climbing fibers, actually blocks the basal chloride permeation across the Deiters' membranes and this effect is partially reversed by its receptor antagonist, alpha-helical CRF [9-41].

Role of different sensory inputs for maintenance of body posture in sitting rat and rabbit

In this paper, we describe the postural activity in sitting rats and rabbits. An animal was positioned on the platform that could be tilted in the frontal plane for up to +/-20-30 degrees, and postural corrections were video recorded. We found that in both rat and rabbit, the postural reactions led to stabilization of the dorsal-side-up trunk orientation. The result of this was that the trunk tilt constituted only approximately 50% (rat) and 25% (rabbit) of the platform tilt. In addition, in the rabbit the head orientation was also stabilized. Trunk stabilization persisted in the animals subjected to the bilateral labyrinthectomy and blindfolding, suggesting that the somatosensory input is primarily responsible for trunk stabilization. Trunk stabilization was due to extension of the limbs on the side moving down, and flexion of the opposite limbs. EMG recordings showed that the limb extension was caused by the active contraction of extensor muscles. We argue that signals from the Golgi tendon organs of the extensor muscles may considerably contribute to elicitation of postural corrective responses to the lateral tilt.

Changes in protein expression in the vestibular nuclei during vestibular compensation

In the guinea pig, labyrinthectomy induces an immediate depression of the resting discharges in the neurons of the ipsilateral vestibular nuclei. Later on, in spite of the persistent deprivation of their ipsilateral labyrinthine input, a spontaneous restoration of activity, which is complete within 1 week, occurs in these neurons. Here, by using computer-assisted quantitative two-dimensional gel analysis, we have detected three proteins whose expressions were increased in the ipsilateral vestibular nuclei 1 week after unilateral labyrinthectomy. The spatio-temporal pattern of this phenomenon was compatible with a role for it in the restoration of activity in the vestibular neurons deprived of their ipsilateral labyrinthine input. Furthermore, the N-terminal amino acid sequences of two of these expressed proteins were obtained.